Coupled Heterogeneous and Homogeneous Hydrocarbon Oxidation on Bimetallic Pt-Pd/Al2O3 Catalysts for Low Temperature Combustion Exhaust

Melanie  Hazlett, University of Houston

Low temperature combustion (LTC) engines are interesting due to gains in fuel economy; however a problem still lies in reducing the emissions from these engines.  In testing oxidation catalysts to treat exhaust from low temperature combustion vehicle engines, it was found that the conditions were such that both homogeneous and heterogeneous oxidation of some hydrocarbons took place.  During homogeneous oxidation in the presence of NO, the NO was easily oxidized to NO2 and the larger hydrocarbon species were partially oxidized to aldehyde and alcohol intermediates.  This homogeneous oxidation has interesting implications for the catalytic oxidation of CO and hydrocarbons on the catalyst, as the NO2 and hydrocarbon intermediates can have a beneficial effect on catalyst performance.  In this study we evaluated the effects these homogeneous reaction products have on oxidation catalyst performance, as well as different hydrocarbon types on the homogeneous reaction itself, in the hopes of exploiting this phenomenon.  Knowing hydrocarbon decomposition temperatures and their NO oxidation ability can lead to an ideal hydrocarbon to preheat and inject upstream of an oxidation catalyst in order to oxidize NO to NO2, which in turn could move CO light off to lower temperatures, as that of the hydrocarbons.

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